GNGTS 2016 - Atti del 35° Convegno Nazionale

20 GNGTS 2016 S essione A matrice Santa”, but then stopped and no more fractures were observed further down along the valley. The Monte Vettoretto structure is presumably affected by a deep seated gravity deformation, that use the Sibillini thrust fault as sliding plane (Fig. 3 above). In fact, the Mt. Vettore normal fault system, in the area of Forca di Presta, crosses and displaces the Sibillini thrust fault for some hundred meters. According to some authors, normal faulting may have locally reutilized some steeper shallow planes of the thrust zone (cfr. “tectonic inversion”; Cooper and Williams, 1989; Calamita et al. , 1994; Pizzi and Galadini, 2009; Di Domenica et al. , 2012 and bibliography therein). In this condition, the discontinuity represented by the limestone block thrusted onto the Laga flysch is a perfect surface for a gravitational decollement. Even the observed post- seismic evolution of the Mt Vettoretto rupture, monitored along the SP34, but even more evident, for example, were the fractures reached the highest elevation across the trail from Forca di Presta to Cima del Redentore (arrow in Fig. 1a), might be evidence of some gravity-driven component of surface fracturing added to fault slip propagation from the deep-seated coseismic slip. So, what we want to stress here is that even in this case, where a sackung -type movement could be advocated, there must be a non-trivial tectonic component in the surface displacement . To explain our thought we use a figure from Serva et al. (2002), explaining the concept of seismic landscape (slightly modified in Dramis and Blumetti, 2005). There are represented the two end member geometry of faults splaying from the seismogenic fault with different dip and emerge at surface not far from the top of fault generated mountain fronts. These two end cases are a Deep Seated Gravitational Slope Deformations (in Fig. 3 indicated by 3 in the A seismic landscape model) and a secondary surface rupture with a very close relation with the seismogenic fault (in Fig. 3 indicated by 2 in the B seismic landscape model). In between, other fault types are possible between the two end cases. Obviously, it is very challenging to distinguish the tectonic and gravitative components of this deformation. In fact, normal fault motion and gravity collapse have the same slip vector, since gravity is the leading force of extensional tectonics (e.g., Doglioni et al. , 2015a, 2015b). In this case, post-seismic monitoring of the deformation is essential also to calibrate Fig. 3 – To summarize in a sketch the geometry of the Cordone del Vettore and M. Vettoretto faults we use a scheme after Serva et al. (2002), explaining the concept of seismic landscape applied to two intermountain basins in Central Italy, different in size, showing also the typical occurrence of coseismic ground effects (after Serva et al. , 2002 and Dramis and Blumetti, 2005). See text for details.